The present invention relates to an optical information recording apparatus, such as an optical disk file unit or optical card file unit, and particularly to a method of recording and reproduction of information using a recording medium available for information overlap recording, and to a recording medium and a recording and reproducing apparatus using the method.
Information systems using optical disks include a reproduction-only type such as the compact disk (CD), video disk, CD-ROM, CDV, etc., and a recording-reproduction type which allows a user to record information. Conventionally, optical disks have been used by a user mostly in two ways. One way of use is in a sense of ROM (read-only memory) in which reproduction-only optical disks such as the CD, video disk and CD-ROM are used by a user for reproducing information which is supplied through mass-produced and relatively inexpensive replica-disks. The other way of use is in a sense of RAM (random access memory) in which a user buys a blank optical disk for creating an optical disk file, records a relatively large quantity of arbitrary information on the disk, adds or rewrites information, and retrieves the information from the disk.
There is known an optical disk which stores the mixture of ROM information and RAM information, in which, as shown in FIG. 2, an optical disk 1 is partitioned in the radial direction into, for example, an area A as a ROM area where ROM information is recorded in advance in the form of pits (phase structure) and an area B as a RAM area which can be recorded arbitrarily by the user. Refer to a Japanese publication NIKKEI ELECTRONICS, No. 443, pp. 88-89, published on Mar. 21, 1988, or JP-A-61-280048, for example.
The optical disk shown in FIG. 2 can store ROM information which is supplied at the purchase and RAM information which is recorded by the user on the same recording medium, and reproduction of ROM information and recording and reproduction of RAM information can take place on a single disk drive unit. However, user-recorded information in the RAM area is often related to some information in the ROM area, and therefore, in operation the optical head needs to move back and forth between the two areas frequently, expending a considerable time for the movement. If it is intended to retrieve information in the ROM area and RAM area concurrently, two optical heads are needed for making simultaneous access to the distant areas, with both optical heads being operated in synchronism, resulting in a complex mechanism.